Accurate Measurement of Boundary Layer Transition in High-Precision Nozzles in Critical Condition.
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概要
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High-precision nozzles whose machining error is less than ±1μm accompanied with a mirror finish were calibrated in critical conditions at pressures up to 0.9MPa against other high-precision nozzles connected in series at the downstream location. Since the Reynolds numbers of the downstream nozzles in a series connection of critical nozzles are lower than that of the upstream one as well as the boundary layer transitions in high-precision nozzles are very stable, the discharge coefficient of the upstream nozzle accompanied with the boundary layer transition could be measured against the downstream nozzles accompanied with the laminar boundary layer. The discharge coefficients of six high-precision nozzles were measured in 14 combinations of the upstream and downstream nozzles at the upstream Reynolds number up to 2.4×106. The boundary layer transitions were detected at the Reynolds number between 0.9×106 and 1.5×106. In the turbulent boundary layer regime, the discharge coefficients of the high-precision nozzles obeyed exactly the newly derived curve, which is expected to be introduced to the revised ISO 9300. The dependence of the discharge coefficient on the Reynolds number during the boundary layer transition were very stable and didn't depend on the nozzle combinations. When all the high-precision nozzles were accompanied with the laminar boundary layers, the mass flowrates calculated from the upstream nozzle and the downstream nozzles based on an unique fitted curve, which had been measured in the laminar boundary layer regime, agreed within -0.02 to +0.05%. This agreement is better than the scattering of the primary calibrations of the high-precision nozzles. Furthermore, it is shown that the high-precision nozzles manufactured in 1992 and 1997 by two different manufacturers had exactly the same discharge coefficient in this regime, therefore, high-precision nozzles are very stable for long period and their characteristics are universal.
- 公益社団法人 計測自動制御学会の論文
公益社団法人 計測自動制御学会 | 論文
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